1. Field of the Invention
The present invention relates to a fluorescent display device in which phosphor-coated anodes arranged in the form of matrix and disposed in groups are adapted to selectively luminesce so as to visually display characters, graphic forms and the like.
2. Description of the Prior Art
The fluorescent display device, in which thermions emitted from a heated filamentary cathode are made to impinge selectively on phosphor-coated anodes so as to visually display characters, graphic forms and the like, is widely used as the display device of electronic equipment or the like, because of its fine color of light emitted, capability of being driven on a low voltage, low power consumption, etc.
Heretofore, fluorescent display devices have been mainly used as numeric-character display devices. In the numeric-character display devices of this type, each pattern display section for one digit is formed of phosphor-coated segment anodes arranged in the shape of the digit 8 and thermions emitted from the cathode are made to impinge selectively on these segment anodes so as to visually display the numerals 0 to 9 as necessary.
The fluorescent display devices of this type have recently become increasingly diversified in the mode of display, as the number of their applications increases. The following examples are of the fluorescent display devices of the matrix type recently developed and put into practical use:
In one example, each pattern display section for one digit is made up of a group of phosphor-coated dot-shaped or rectangular anodes arranged in the form of matrix and these anodes are selectively bombarded with electrons so as to visually display characters and numeric characters. In another example, equally-spaced anodes are arranged in the form of matrix throughout the entire display surface so that graphic forms can be displayed. In still another example, a scanning means is provided to continuously move visually-displayed characters and graphic forms in a predetermined direction so as to improve the effect of display.
An example of the fluorescent display device of the matrix type is shown in FIG. 1, in which the arrangement of the groups of anodes and that of control electrodes are given. In FIG. 1, reference numeral 1 designates phosphor-coated anodes arranged on a substrate (not shown) in the form of matrix. The anodes 1 are electrically connected together by anode wires 2 on a row-by-row basis. In other words, the anodes 1 on the same row of the matrix are electrically connected together by each anode wire 2. Control electrodes 3, or grids, are disposed above the anodes 1 on a column-by-column basis. In other words, each of the control electrodes 3 is disposed above the anodes 1 disposed on each column of the matrix. The control electrodes 3 is in the form of, for instance, mesh-shape so that light emitted from the anodes 1 can be clearly seen, being connected to external terminals 4 respectively.
Thus, if an anode signal is given selectively to the anode wires 2 and a control signal is given selectively to the control electrodes 3, electrons emitted from the cathode (not shown) impinge on the anodes 2 positioned at points where the anode wires 2 to which the anode signal is selectively given intersect with the control electrodes 3 to which the control signal is selectively given, and thereby characters or graphic forms are visually displayed.
In addition, characters and graphic forms displayed can be continuously moved by the following method:
The control electrodes 3 are scanned successively at regular intervals. According to this scanning of the control electrodes 3, the anode wires 2 to which the anode signal is given are cyclically changed. In this manner, the continuously-moving display can be realized.
However, the conventional fluorescent display device of the matrix type shown in FIG. 1 has the following problems and disadvantages:
In order to display characters, graphic forms and the like in a more natural and accurate form, it is required to increase the number of anodes 1. The increase in the number of the anodes 1 results in the increase in the number of the anode wires 2 and that of the external terminals 4 for giving the control signal to the control electrodes 3. In other words, the number of external terminals for giving drive signals to various electrodes becomes extremely large. As a result, the production process becomes complicated and the assembly accuracy required becomes high. For instance, if the matrix of anodes 1 consists of m rows and n columns, the number of external terminals required is equal to "m+n+2" including the number of external terminals for the cathode. Therefore, it is required to lead this number of external terminals outside of the periphery of the substrate.
In addition, the unselected control electrodes 3 (i.e., the control electrodes 3 to which the control signal is not given) are usually kept at a negative potential lower than the cathode potential, and therefore negative electric fields formed by these unselected control grids 3 have influence on the passage of electrons impinging on the selected anodes 1. For instance, if an unselected control electrode 3 is adjacent to a luminescing anode 1, a region on which electrons cannot impinge, or a display defect, will occur at the edge of the luminescing anode 1. Especially, when the anodes 1 are arranged at close intervals so as to perform accurate display, the above-mentioned display defects are liable to occur, resulting in the deterioration of the display quality.